A form image managing system for reading a paper form with an image scanner device, for putting the read form into an electronic document, and for retaining obtained form image data as trail information is known. With such a form managing system, the capacity of a storage device for retaining form image data is bloated, leading to a system cost increase and complexity of system operations. For this reason, reductions in the amount of form image data retained in a storage device are demanded. On the other hand, however, an image quality level that is so high as to be available as trail information is demanded for an original form image reproduced from the retained form image data.
For reductions in the amount of form image data, the amount of form image data is compressed, byway of example, with a still image compression technique such as Joint Photographic Experts Group (JPEG) system. However, the bloating of storage capacities in recent form managing systems is serious, and it cannot be said that measures using a data compression rate obtained by applying a still image compression technique are not sufficient against the bloating of storage capacities under present circumstances.
Incidentally, as another technique for reducing the amount of form image data, a technique for generating a difference image between an image of a known form where data is not written and an image of the form after data is written, and for recording the difference image data with a recording device is known.
Also a technique for reducing the amount of information of a difference image generated as described above is known. With this technique, identification is initially made between a character area and other areas in a script image of an electronic document. Next, identification is made between a character area and other areas in an image superimposed by handwriting the electronic document. Then, the amount of a position shift is detected between each of the areas in the script image and each of the areas in the superimposed image, and a difference process is executed by correcting a position based on the detected amount of a position shift, thereby preventing a subtraction from being incompletely performed in the difference process. However, this technique is a technique for recording only a hand-written portion, and subsequent reproduction of the superimposed image is not taken into account. Accordingly, this technique is not suitable for a use application intended to handle recorded data as trail information the originality of which needs to be assured. Moreover, with this technique, a position of an image of a known form and that of an image of the form after data is written are aligned in order to reduce the amount of difference image data. Therefore, this technique needs complicated process steps of initially making an identification between a character area and other areas in each of two images, of aligning positions of the images after obtaining the amount of a position shift between the images based on an identification result, and of generating a difference image thereafter.
In addition, a form management technique is known. With this technique, when a form name is selected, a print medium on which an image of the selected form and a barcode indicating its retention location name are printed is output, and the image of the form is stored in the retention location indicated by the barcode when an image where data is written is input to the print medium.
Furthermore, a form creation technique is known. With this technique, a form ID of a form to be created is generated based on a template ID created from a form template and a form data ID created from overlaying form data, and the form template of the form to be generated and the form data are managed to be identifiable.
Still further, a technique for preventing information of a common portion within derived documents from being scattered when the derived documents are created by partially changing a master document is known. With this technique, difference information that indicates contents of a change made to a plurality of blocks into which the master document is partitioned, and information that identifies a block including the changed portion are retained as information of the derived documents.
Techniques described in the following documents are known.    Document 1: Japanese Laid-open Patent Publication No. H11-175701    Document 2: Japanese Laid-open Patent Publication No. 2004-287682    Document 3: Japanese Laid-open Patent Publication No. H10-162087    Document 4: Japanese Laid-open Patent Publication No. 2009-110387    Document 5: Japanese Laid-open Patent Publication No. 2008-117051